Chub Mackerel Scomber Japonicus Research Articles

Acoustic Target Strengths and Swimbladder Morphology of Chub Mackerel Scomber japonicus in the Northwest Pacific Ocean

The Northwest Pacific chub mackerel (Scomber japonicus) is one of the most productive, economically important fishery resources worldwide. Accurately assessing this species and ensuring adherence to total allowable catch limits are crucial owing to fluctuations in their abundance and distribution. Acoustic target strength measurements of S. japonicus were conducted at 38, 70, and 120 kHz using a split-beam echosounder of individuals from nine size groups (mean fork length, 10.8–28.3 cm) swimming freely in a net cage within a seawater tank. An underwater camera was utilized to simultaneously measure swimming angle. Least-squares regression analysis revealed that when the slope was constrained to 20, as per the generally applicable morphometric equation, the resulting values for the constant term (b20) were −67.7, −66.6, and −67.3 dB at 38, 70, and 120 kHz, respectively. S. japonicus mean swimming angle across the groups was −10.5–9.6° (standard deviation [SD], 16.3–33.3°). Furthermore, the ratio of swimbladder height to swimbladder length, the ratio of swimbladder length to fork length, and the tilt angle of the swimbladder (mean ± SD) were 0.191 ± 0.060, 0.245 ± 0.055, and 9.6 ± 3.0°, respectively. These results can be used for the acoustic stock assessment of S. japonicus in the Northwest Pacific Ocean.

A Study on the Impact of Environmental Factors on Chub Mackerel Scomber japonicus Fishing Grounds Based on a Linear Mixed Model

Chub mackerel (Scomber japonicus) is a commercially important fish species which are widely distributed in the North Pacific. Based on the fishery data from China’s high-sea light-purse seine fishing from 2014 to 2020 and the marine environment factors, a mixed linear model considering the actual spatiotemporal stratification of the catch per unit effort (CPUE) was established to analyze the fixed and random effects of marine environmental factors on the CPUE of chub mackerel and to investigate the relationship between the abundance of chub mackerel resources in the Northwest Pacific and two marine environmental factors: sea surface temperature (SST) and chlorophyll-a concentration (CHL). The results showed that SST had a significant fixed effect on the CPUE. In contrast, the natural logarithm of chlorophyll (logCHL) had no fixed effect on the CPUE. Based on the monthly analysis, random fluctuations were observed in the impact of logCHL on the CPUE. LogCHL and CPUE show a positive correlation during spawning and wintering periods and a negative correlation during the feeding period. The study showed that when fishery sampling data exhibit spatiotemporal stratification, linear mixed models can effectively incorporate both the fixed and random effects of environmental factors on the CPUE of chub mackerel. Linear mixed models can play an important role in analyzing the fluctuations in resource abundance and the mechanisms governing the formation of fishing grounds for chub mackerel in the Northwest Pacific.

Ichthyocenosis of the upper epipelagic layer in the Pacific waters of Russia during japanese sar-dine «renaissance» in the beginning of the 21<sup>st</sup> century

Dynamics of integral parameters for the species structure in ichthyocenosis of the upper epipelagic layer in the Pacific waters off the Kuril Islands in 2019–2023 is discussed in compare with previously published data since 2004 in context of a new bloom of japanese sardine Sardinops melanostictus. Results of trawl surveys are clustered using the method of multi-dimensional scaling. Species composition in the trawl catches in 2004–2013, before the time of mass expansion of subtropi-cal migrants, as japanese sardine and chub mackerel Scomber japonicus, was distinguished by domina-tion of mesopelagic fishes of families Myctophidae and Microstomatidae and pink salmon Oncorhynchus gorbuscha. From 2014 to the present, the dominant positions in the ichthyocenosis were held by japanese sardine and chub mackerel, with a decreasing role of the latter. In the last pentade (2019–2023), the species structure of pelagic ichthyocenosis in the Pacific waters of Russia has not undergone fundamental changes. At the same time, the tendency has increased for uneven distribution of biomass between the species of fish community in favor of japanese sardine. The polydominance index decreased significantly (P < 0.05, t-test 4.33) from 4.85 ± 0.44 in 2004–2013 to 2.37 ± 0.21 in 2019–2022, and the index of evenness of species structure decreased from 0.41 ± 0.04 to 0.15 ± 0.02 (P < 0.05, t-criterion 5.25). Growth of domestic and foreign catches of japanese sardine in the second decade of the 21 century is a sign of this species bloom beginning.

Spatiotemporal analysis of marine environmental influence on the distribution of chub mackerel in the Northwest Pacific Ocean based on geographical and temporal weighted regression

In order to further analyze the impact of the marine environment factors in the Northwest Pacific Ocean on the distribution of chub mackerel Scomberjaponicus resources, a spatio-temporal weighted regression model was constructed based on the marine environmental and fishery data of China's light purse seine production in the high seas of the Northwest Pacific Ocean. Six environmental factors, including sea surface temperature (SST), chlorophyll a concentration (Chl-a), eddy kinetic energy (EKE), SST gradient intensity (GSST), longitudinal SST gradient (xGSST) and latitudinal SST gradient (yGSST) in spring, summer and autumn were used to analyze the impact of the temporal and spatial environmental factors on chub mackerel. The results show that the statistically significant variables (p < 0.05) were different in seasonal models. The SST, Chl-a, yGSST and EKE were statistically significant in the spring model, SST, yGSST and GSST in the summer model, and EKE, yGSST and GSST in the autumn model. The adjusted coefficients of determination (R2adj.) of the spring, summer and autumn models were 0.488, 0.378 and 0.475, respectively. The results suggest that the coefficients of various environmental factors changed not only with time, but also with geographical location. Through this study, we can provide methodological reference for the study of resource change and fishery formation mechanism of chub mackerel fishery in the Northwest Pacific Ocean.

Relationship between stable cesium concentration and body size of Japanese flounder Paralichthys olivaceus and the effect of a size-dependent shift in diet.

To understand the relationship between the radioactive cesium (Cs) concentration in muscle of Japanese flounder Paralichthys olivaceus and the species' biological characteristics (size, sex, and age) under conditions of ecological equilibrium (i.e., distributed among ecosystem components over sufficient time, and with nearly constant ratios of Cs concentration in organisms to the concentration in water) as existed before the accident at the Fukushima Dai-ichi Nuclear Power Station (FDNPS), Japan, in 2011, we examined stable Cs, as it is thought to exist in equilibrium in the environment and behave similarly to radioactive Cs in aquatic animals. The concentration of stable Cs in 241 P. olivaceus (range 216-782 mm total length [TL]) collected in Sendai Bay, approximately 90 km north of the FDNPS, in June-July 2015 was expressed as an exponential function with size as an independent variable; the results show the concentration of stable Cs doubled with an increase in TL of 442 mm. Next, to evaluate the cause of the size-dependent change in stable Cs concentration, we examined 909 individuals (200-770 mm TL) collected in September 2013-July 2015 to determine their feeding habit based on size. Analysis of the frequency of occurrence of prey organisms in stomach contents showed that sand lance Ammodytes japonicus (55-180 mm standard length [SL]) was the most consistently consumed across size classes. Analysis on a wet-mass basis showed that A. japonicus and anchovy Engraulis japonicus (65-130 mm SL) were the main food of P. olivaceus sized 200-599 mm TL, whereas chub mackerel Scomber japonicus (120-230 mm SL) and two species of flatfishes (180-205 mm SL) were abundant in the diet of P. olivaceus sized ≥600 mm TL. All these prey items were presumed to have similar concentrations of stable Cs. Based on the above, the effect of diet on the relationship between stable Cs in muscle and fish size was considered negligible. That the diet of P. olivaceus largely did not change with size was also confirmed by C and N stable isotope ratios in P. olivaceus and their prey species. Therefore, the Cs-size relationship is probably determined by changes in the balance between the rate of Cs intake from food and seawater and the excretion rate during growth, both of which change as functions of body mass. Values of stable Cs concentrations among environmental components and animals appear to be a valid indicator for understanding the radioactive Cs distribution in the marine environment and aquatic animals under the equilibrium state, as existed before the 2011 nuclear accident.

Practical target strength of free-swimming chub mackerel Scomber japonicus

Practical target strength of free-swimming chub mackerel Scomber japonicus

Early life history traits of chub mackerel Scomber japonicus in the Oyashio water revealed by otolith microstructure

Early life history traits of chub mackerel Scomber japonicus in the Oyashio water revealed by otolith microstructure

Environmental DNA in the Kuroshio reveals environment-dependent distribution of economically important small pelagic fish

IntroductionSmall pelagic fishes constitute large proportions of fisheries and are important components linking lower and higher trophic levels in marine ecosystems. Many small pelagic fishes in the Northwest Pacific spawn upstream in the Kuroshio and spend their juvenile stage in the Kuroshio Front area, indicating that the Kuroshio Current system impacts their stock fluctuations. However, the distribution of these fish relative to the Kuroshio has not been determined due to dynamic spatio-temporal fluctuations of the system. Here, the recent development of environmental DNA (eDNA) monitoring enabled us to investigate the distribution patterns of four economically important small pelagic fishes (Japanese sardine Sardinops melanostictus, Japanese anchovy Engraulis japonicus, chub mackerel Scomber japonicus, and blue mackerel Scomber australasicus) in the Kuroshio Current system. MethodsThe influence of environmental factors, such as sea water temperature, salinity, oxygen concentration, chlorophyll-a concentration, and prey fish on the occurrence and quantity of target fish eDNA was analyzed using generalized additive models. In addition, the detection (presence) of target fish eDNA were compared between the offshore and inshore side areas of the Kuroshio axis.ResultsSea water temperature showed important effect, especially on the distribution of Japanese sardine and Japanese anchovy, whereas the distribution pattern of chub mackerel and blue mackerel was greatly influenced by the eDNA quantity of Japanese sardine and Japanese anchovy (especially potential prey fish: Japanese anchovy). In addition, we found that the four target fish species could be observed in areas on the inshore side or around the Kuroshio axis, while they were hardly found on the offshore side.ConclusionBased on eDNA data, we succeeded in revealing detailed spatial distribution patterns of small pelagic fishes in the Kuroshio Current system and hypothesized predator–prey relationships influence their distribution in small pelagic fish communities.

Metabarcoding of ichthyoplankton communities associated with a highly dynamic shelf region of the southwest Indian Ocean.

Drifting fish eggs and larvae (ichthyoplankton) can be identified to species using DNA metabarcoding, thus allowing for post hoc community analyses at a high taxonomic resolution. We undertook a regional-scale study of ichthyoplankton distribution along the east coast of South Africa, focused on the contrasting environments of the tropical Delagoa and subtropical Natal Ecoregions, and on exposed and sheltered shelf areas. Zooplankton samples were collected with tow nets at discrete stations along cross-shelf transects (20-200 m depth) spaced along a latitudinal gradient that incorporates a known biogeographical boundary. Metabarcoding detected 67 fish species, of which 64 matched prior distribution records of fishes from South Africa, with the remaining three known from the Western Indian Ocean. Coastal, neritic and oceanic species were present, from epi- and mesopelagic to benthopelagic and benthic adult habitats. By family, Myctophidae (10 species), Carangidae, Clupeidae, Labridae (each with 4 species) and Haemulidae (3 species) were most speciose. Ichthyoplankton community composition varied significantly with latitude, distance to coast, and distance to the shelf edge. Small pelagic fishes had the highest frequency of occurrence: Engraulis capensis, Emmelichthys nitidus and Benthosema pterotum increased in frequency towards the north, whereas Etrumeus whiteheadi increased towards the south. Chub mackerel Scomber japonicus accounted for most variability related to distance from the coast, whilst African scad Trachurus delagoa correlated with distance to the shelf edge. Dissimilarity between communities in the Delagoa and Natal Ecoregions was 98-100%, whereas neighbouring transects located within the sheltered KwaZulu-Natal Bight had lower dissimilarity (56-86%). Onshore transport of ichthyoplankton by Agulhas Current intrusions plausibly explained the abundance of mesopelagic species over the shelf. Metabarcoding followed by community analysis revealed a latitudinal gradient in the ichthyoplankton, associations with coastal and shelf-edge processes, and evidence of a spawning area in the sheltered KwaZulu-Natal Bight.

Vertical migration patterns linked to body and environmental temperatures in chub mackerel

Fishes in the genus Scomber are currently one of the most abundant, economically important, and widely distributed fishes in the North Pacific and North Atlantic Oceans. This study recorded the depth, peritoneal and environmental temperature of the chub mackerel Scomber japonicus using an electronic tag. The 176 tagged mackerel were released from Tsushima Strait, Japan. A total of 1,075 days of data from November to August were obtained from seven individuals. Mackerel extensively used the epipelagic zone, and ranges of depth and environmental temperature during the overall recording period were 0.5–213 m and 3.4–29.1 °C, respectively. The mean depth during the day was deeper than that observed during the night in the foraging season. This vertical distribution pattern of the mackerel may overlap with that of prey organisms. We also observed a unique short-term vertical migration of mackerel during the foraging season. When the mackerel repeated the short-term vertical migrations, ranges of peritoneal temperature (13.9–15.0 °C) were narrower than environmental temperature (7.9–16.5 °C). This behavior allowed the mackerel to use physiologically unsuitable thermal layers, while avoiding overcooling of body temperature. However, these vertical migration patterns broke down in the spawning season. Behavioral decisions of diel vertical migration in chub mackerel may be affected by body condition of individual fish such as maturation states. Quantifying vertical migrations of Scomber species occupying intermediate trophic levels is important when considering conservation strategies of more than simply fisheries stock but also that of marine ecosystems.

Biological interactions potentially alter the large-scale distribution pattern of the small pelagic fish, Pacific saury Cololabis saira

We aimed to understand the effect of biological interactions on the distribution of small pelagic fishes. Surveys were conducted during 2003-2019 using sea surface trawl nets in the western and central North Pacific Ocean, covering an area between 143° E and 165° W, to estimate the distributions of 4 small pelagic fishes: Pacific saury Cololabis saira, Japanese sardine Sardinops melanostictus, chub mackerel Scomber japonicus, and Japanese anchovy Engraulis japonicus. These species are potential competitors, as they all occupy a similar niche. Japanese anchovy was abundant during 2003-2012, while Japanese sardine and chub mackerel were abundant during 2013-2019. Only Pacific saury was distributed throughout the survey area, while the others occurred within the area west of 180° longitude (WA). Pacific saury and its potential competitors showed adjacent distributions, with a slight overlap along sea surface temperature gradients in the WA. This distribution pattern remained even when Japanese sardine expanded its distribution to colder waters and increased in abundance after 2013, resulting in a shift in the distribution of Pacific saury to colder waters and a period of high densities of Japanese sardine. Such a distribution shift of Pacific saury was not observed in the area east of 180° longitude, where no Japanese sardine was observed. These results suggest the possibility that biological interactions such as inter-species competition can be an important factor in determining the distribution of small pelagic fishes.

Little evidence for bioaccumulation or biomagnification of microplastics in a deep-sea food web

Microplastic contamination is documented in marine organisms, but little is known about bioaccumulation or biomagnification of microplastics, especially in tissues external to the gastro-intestinal (GI) tract. The objective of this work was to explore microplastic contamination in GI tracts and other tissues (abdomen and tail in crustaceans; mantle in cephalopods; fillets in fishes) of species at different trophic levels sampled in a deep-sea food web in Monterey Bay, CA, USA. The species included are tuna crab Pleuroncodes planipes, market squid Doryteuthis opalescens, northern lampfish Stenobrachius leucopsarus, chub mackerel Scomber japonicus, California halibut Paralichthys californicus, and Chinook salmon Oncorhynchus tshawytscha. After chemical digestion, microplastics in GI tracts were quantified and identified to material type using μ-Raman spectroscopy and in other tissues using pyrolysis-GC/MS. The concentrations of microplastics in GI tracts were significantly different among species, and microplastic contamination was dominated by microfibers. The concentrations of microplastics (mainly polyethylene and polyvinyl chloride) in other tissues also varied among species. A significant positive correlation between body size and plastic concentration in other tissues was observed for halibut only, suggesting bioaccumulation may not be ubiquitous. The trophic magnification factor for microplastics beyond the GI tract was &lt;1, suggesting that biomagnification is not occurring in tissues. However, we did observe evidence for biomagnification of microplastics in the GI tracts. Future studies are needed to better understand these patterns and the mechanisms for translocation, bioaccumulation, and biomagnification of microplastics in aquatic organisms.

Density-dependent attributes of schooling in small pelagic fishes.

Many small pelagic fishes obligately form schools; some of these schools reach remarkable sizes. Although the school is a fundamental and important ecological unit and is the site of biological interactions such as competition and predation, information on schooling processes in the field remains scarce. Here, we examined the quantitative relationships between population density and school size, the number of schools, and other school characteristics (i.e. packing density, volume, and cross-sectional area) in three species of small pelagic fishes: Japanese anchovy Engraulis japonicus, Japanese sardine Sardinops melanostictus, and chub mackerel Scomber japonicus. We found that school size increased almost linearly with population density, whereas the number of schools and other characteristics increased non-linearly with population density, whereby the rate of increase slowed radically as population density increased. These results indicate that, at low population densities, an increase in density causes an increase in both school size and the number of schools, whereas at higher population densities, an increase in density triggers the formation of larger schools rather than more schools. Furthermore, we found that the shapes of the relationships of all school characteristics with population density differed amongst species. Our results indicate that the schooling behaviour of small pelagic fishes is density-dependent, and responses to changes in density are species-specific. Our results provide insight into how biological interactions such as intra- and inter-specific competition and predator-prey interactions mediate the density-dependent processes that underlie the population dynamics and community structure of small pelagic fishes in marine ecosystems.

Assessing the reliability of species distribution models in the face of climate and ecosystem regime shifts: Small pelagic fishes in the California Current System

Species distribution models (SDMs) are a commonly used tool, which when combined with earth system models (ESMs), can project changes in organismal occurrence, abundance, and phenology under climate change. An often untested assumption of SDMs is that relationships between organisms and the environment are stationary. To evaluate this assumption, we examined whether patterns of distribution among larvae of four small pelagic fishes (Pacific sardine Sardinops sagax, northern anchovy Engraulis mordax, jack mackerel Trachurus symmetricus, chub mackerel Scomber japonicus) in the California Current remained steady across time periods defined by climate regimes, changes in secondary productivity, and breakpoints in time series of spawning stock biomass (SSB). Generalized additive models (GAMs) were constructed separately for each period using temperature, salinity, dissolved oxygen (DO), and mesozooplankton volume as predictors of larval occurrence. We assessed non-stationarity based on changes in six metrics: 1) variables included in SDMs; 2) whether a variable exhibited a linear or non-linear form; 3) rank order of deviance explained by variables; 4) response curve shape; 5) degree of responsiveness of fishes to a variable; 6) range of environmental variables associated with maximum larval occurrence. Across all species and time periods, non-stationarity was ubiquitous, affecting at least one of the six indicators. Rank order of environmental variables, response curve shape, and oceanic conditions associated with peak larval occurrence were the indicators most subject to change. Non-stationarity was most common among regimes defined by changes in fish SSB. The relationships between larvae and DO were somewhat more likely to change across periods, whereas the relationships between fishes and temperature were more stable. Respectively, S. sagax, T. symmetricus, S. japonicus, and E. mordax exhibited non-stationarity across 89%, 67%, 50%, and 50% of indicators. For all species except E. mordax, inter-model variability had a larger impact on projected habitat suitability for larval fishes than differences between two climate change scenarios (SSP1-2.6 and SSP5-8.5), implying that subtle differences in model formulation could have amplified future effects. These results suggest that the widespread non-stationarity in how fishes utilize their environment could hamper our ability to reliably project how species will respond to climatic change.

Development of sandwich enzyme-linked immunosorbent assays for chub mackerel Scomber japonicus gonadotropins and regulation of their secretion in female reproduction

The pituitary gonadotropins (Gths), follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh), play critical roles in regulating gonadal development and sexual maturation in vertebrates. We developed non-competitive enzyme-linked immunosorbent assays (ELISAs) to measure Fsh and Lh in chub mackerel Scomber japonicus, which is a commercially important scombrid species. Mouse monoclonal antibodies specific for Fsh and Lh, and a rabbit polyclonal antibody against both Gths were produced by immunization with hormones purified from chub mackerel pituitaries. These monoclonal and polyclonal antibodies were used as capture and detection antibodies in the developed sandwich ELISAs. The ELISAs were reproducible, sensitive, and specific for chub mackerel Fsh and Lh. Parallelism between the standard curve and serial dilutions of chub mackerel serum and pituitary extract was observed for both Fsh and Lh ELISAs. Comparison between vitellogenic and immature females revealed that Fsh is secreted during vitellogenesis and Lh is barely released during immaturity. After gonadotropin-releasing hormone analog (GnRHa) injection, vitellogenic females showed increases in serum Lh, whereas serum levels of Fsh did not vary. Moreover, the serum steroid profiles revealed that estradiol-17β was continuously produced after GnRHa treatment, whereas 17,20β-dihydroxy-4-pregnen-3-one secretion was transiently induced. These results indicate that, in vitellogenic females, GnRHa stimulates the release of Lh, but not Fsh, which results in acceleration of vitellogenesis and induction of oocyte maturation via steroid production.

Application of a Length-Based Stock Assessment Model for the Chub Mackerel (Scomber japonicus) in Korean Waters

Application of a Length-Based Stock Assessment Model for the Chub Mackerel (Scomber japonicus) in Korean Waters

Impacts of Morphological Characteristics on Target Strength of Chub Mackerel (Scomber japonicus) in the Northwest Pacific Ocean

Chub mackerel (Scomber japonicus) is an important commercial fish in the Northwest Pacific Ocean. Accurate target strength (TS) underpins acoustic stock assessment but the TS of S. japonicus is still poorly understood. In this study, the Kirchhoff-ray mode (KRM) model was used to estimate the TS of S. japonicus and its relationship with sound wave frequency and fish morphology. The results revealed that TS values varied with pitch angle shifts, with the impact on fish scattering strength being greater at higher frequency. This is less important because 38 kHz has been used for the biomass assessment of these fish resources. At frequencies of 38 kHz, 70 kHz, 120 kHz and 200 kHz, TS was greatest at a pitch angle range of -10° to 0°, which was related to the angle of the swim bladder tilt. There were almost no differences between TS estimated using the measured pitch angle distributions and using the universal distribution. When the measured pitch angle was N[-3°,4°], the average TS of S. japonicus with body length of 12.04–22.17 cm at four frequencies was -48.88 dB, -49.14 dB, -49.75 dB and -48.55 dB, respectively. The regression intercept (b20) in TS–body length equation was -73.27 dB, -73.56 dB, -74.18 dB and -73.46 dB, respectively. Variation in TS range at 0–300 m depth was about 10 dB. The simulated broadband target strength spectrum shows the scattering characteristics of individuals with different swim bladder length between 0–250 kHz. These results could be used for identification of S. japonicus in echograms and provide reference for acoustic stock assessment of S. japonicus in the Northwest Pacific Ocean.

Industry-initiated catch limit management: The case of purse seine fishery in Japan’s EEZ waters of the North Pacific Ocean

The need for effective fishery management is growing worldwide due to the overexploited status of many fishery resources. While co-management between the government and fishers is considered a viable option, the performance of such a management is not well understood. This study describes the historical context, the current situation, and the price changes associated with the mackerel (chub mackerel Scomber japonicus, blue mackerel Scomber australasicus) purse seine fishery management in Japan’s EEZ waters of the North Pacific Ocean. This fishery is unusual in that an industry organization plays a major role in managing the total allowable catch (TAC) set by the government. Notably, the organization voluntarily introduced vessel-level monthly catch limits (CL) in 2007. This co-management system has been effective in adhering to the TAC. Moreover, we examine the price changes associated with the CL management by using difference-in-differences design where the prices in ports where vessels under the CL management land and where they do not are compared before and after 2007. Results indicate that the introduction of this management is associated with an increase in their mackerel price by 21.335 yen/kg (s.e. = 10.397), which virtually eliminated the price gaps with mackerel in other regions in Japan. Controlling for income, export price, and time trends do not change our result quantitatively. However, further study is needed to clarify the causal impact of the CL management, as the common trend assumption is likely to hold but the stable unit treatment value assumption is likely not in our setting.

Effects of formalin preservation on egg size of small pelagic fish as major target species in ichthyoplankton surveys

AbstractPreservation is critical for egg and larval samples from ichthyoplankton surveys. As growing interest is directed toward maternal effects on egg quality, historical collections of egg samples in formalin are potentially invaluable materials but concerns about the effects of formalin preservation need to be clarified. The present study examined effects of formalin preservation on egg size of Japanese sardine Sardinops melanostictus, chub mackerel Scomber japonicus and Japanese anchovy Engraulis japonicus over a long period (30–36 months). Overall, the egg sizes slightly decreased in a couple of months after preservation but then recovered to be at a similar level to the live eggs for diameters of spherical eggs of sardine and mackerel and short diameters of ellipsoidal eggs of anchovy, although a caveat lies in unstable and slightly increasing patterns in long diameters of anchovy eggs. No substantial differences were found between 5% and 10% formalin solutions. For practical purposes, we conclude that no correction factors are required for using the measurements of egg samples preserved in formalin over a long period. Assuming the applicability to congeneric species, the information presented here supports the validity of previous studies and will promote future studies on egg size variability in small pelagic fish based on historical collections of egg samples preserved in formalin in various regions of the world.

Effects of Initial Freshness Level, Frozen Storage Temperature, and Storage Period on Lipid Deterioration and K-value in Meat Blocks from Chub Mackerel Scomber japonicus

ABSTRACT The effects of freshness level of raw materials, frozen temperature, and storage period on lipid oxidation and K-value of chub mackerel Scomber japonicus meat during frozen storage, were investigated. When the chub mackerel meat was stored at −20°C for 12 months, the peroxide values (PVs) of the low-freshness group (LG) were significantly higher than the medium-freshness group (MG) and the high-freshness group (HG), respectively. The K-value of LG was significantly higher than MG and HG. However, when storage was at −30°C, the PVs of HG were at the same level as that of MG but were slightly lower than LG. In contrast, the K-values of samples did not change at this storage temperature. These results indicate that the quality of chub mackerel before freezing was improved by human handling and that the quality was maintained at a high freshness even when they were stored at −20°C for 12 months.